The present invention relates to a continuous process for the preparation of copolycarbonate resins. More particularly, the present invention relates to a continuous process for the preparation of copolycarbonate resins having the following advantages, especially upon preparing molding materials of intricate structure and of thin-wall:
1) they can easily be processed at relatively low temperatures;
2) they have excellent impact strength, especially at low temperatures; and
3) they have excellent melt flow that is 2 to 3 times greater than that of the conventional polycarbonates.
In general, aromatic polycarbonates possessing excellent mechanical and physical properties of tensile strength, dimensional stability, heat and impact resistance and optical clarity, have been widely used in numerous industries. However, in comparison with other polymers, the polycarbonates have a relatively higher melt viscosity during the manufacturing process leading to poor operations. There are also the difficulties in preparing intricate structures and thin-wall molding materials.
Many attempts to overcome the above problems have been continued until recently. Yet, it was not easy to retain all of the advantages of the conventional polycarbonates, and simultaneously to make lower the viscosity in a molten state.
One example of such attempts is the use of plasticizer for the very first time. Although fluidity of polycarbonate is generally enhanced when the plasticizer is used in conjunction with thermoplastic resins, use of the plasticizer induces brittleness and depreciation of the conventional physical properties of the thermoplastic resins.
Another examples are to use a molecular weight regulator, which is substituted phenol species containing a long aliphatic chain, or to prepare a low molecular weight polymer to improve the melt flow of the polymer. However, Notched Izod Impact Strength of the polymer is decreased and brittleness is induced in the polymer. Thus, the desired characteristics of the polymer may not be obtained.
Alternatively, application of bisphenol-A derivatives having a long aliphatic chain contributes to a significant increase in the melt flow. However, high costs of starting materials and low Notched Izod Impact Strength of the polymer are also another problems.
Meanwhile, the blending of the polycarbonates with other polymers results in improvement of their melt flow. But, another adverse effects on properties are obtained such as deterioration of clarity of the polycarbonates. Thus, the above method could not solve the existing problems.
Knowing that aforementioned problems have limitations, U.S. Pat. No. 3,169,121 (Goldberg et al.) discloses that a soft segment (molecules having a good mobility) with a long chain of an aliphatic ester derivative is incorporated into a part of polymer chain comprised of only a hard segment (molecules having a low mobility) i.e. bisphenol-A, which makes it possible to obtain copolycarbonate exhibiting a low glass transition temperature(Tg) and an improved melt flow. Additionally, it has been found that aliphatic diacid derivatives are preferred as aliphatic ester derivatives.
However, the above patent uses pyridine solvent and aliphatic diacid chloride, which is an aliphatic diester derivative with color. Thus, it brings about a problem with a color formation of the resulting product. Accordingly, the following problems still exist in the above patent: 1) Removal of pyridine solvent from the polymer during the preparation process; 2) color retention of the resulting product; 3) a high cost of aliphatic diacid chloride; and 4) mass supply of starting materials at the commercial level.
Accordingly, ongoing studies have been conducted to focus on the starting materials containing long aliphatic chains, while an interfacial process is used to solve the problems with the color retention and removal of the solvent, simultaneously. It has been found that an aliphatic diacid salt is a suitable material (comonomer) since its raw material is relatively easily available and it is also inexpensive. Kochanowski (U.S. Pat. No. 4,286,083) is one of the researchers who have used these materials and adopted the interfacial process for his experiment. In this patent, phosgenation reaction, in which two monomers (for example, bisphenol-A and aliphatic diacid derivative) exhibiting differences of reactivity are used, can be completed upon controlling a pH at two different stages. It discloses that polyester carbonate having low glass transition temperature(Tg) can be obtained.
Specifically, the phosgenation of aliphatic diacid and bisphenol-A at from pH 4.5 to 8, preferably from pH 5.5 to 6.5, is carried out to convert said aliphatic diacid into aliphatic diacid chloride, which is then reacted with bisphenol-A, the pH of the reaction is raised to a value of between 9 and 11.5 for the completion of the oligomerization and polycondensation reactions.
However, only 50% of adipic acid, which is used as an amount of 10 mole % of bisphenol-A (the principal monomer), is incorporated into the polymer backbone.
Even though the pH is controlled at two stepwise ranges for the completion of the reactions, unreacted reactants still remain in abundance. Moreover, a batch-type process for controlling the pH makes lessen the productivity of polycarbonates in the process, in comparison with a continuous-type process.
Other attempts have been made to improve Kochanowski""s method in part. U.S. Pat. No. 4,677,183 discloses that a diacid salt rather than a diacid of a neutral state can improve the current rate of reaction. However, this method also uses the batch-type process, and a pH should be controlled at 2 stages in order to minimize any side reactions and increase the reaction rate.
On the other hand, other efforts, which include incorporation of aliphatic ester derivatives with long chains that act as a soft segment portion into polymer chains and simultaneously end-capping of the polymers using phenol derivatives substituted with paracumyl, isooctyl and isononyl, are made to obtain great improvements in physical properties of copolyestercarbonates (U.S. Pat. Nos. 4,774,315 and 4,788,275). However, these inventions have shortcomings that these also use the batch-type process and a pH should be controlled to two different stages for reacting reactants.
The above efforts result in partial improvements in polymers through modification of conventional polycarbonates exhibiting a high viscosity in its melting state upon processing. However, the problems such as simplification of the preparation process and increase of the reaction rate remain still unsolved. A novel polymerization process is required for simplification of the preparation process while inserting a co-monomer having different reactivity into the backbone of polymer.
In the prior art, a carbonate precursor (phosgene) should be introduced divisionally at two different pH ranges during the phosgenation process in order that monomers having different reactivity (i.e. bisphenol-A and aliphatic diacid salt derivative) are reacted with the carbonate precursor, which results in reducing unreacted reactants and improving melt flow of a conventional polycarbonate. For this process, only the batch-type process has been applicable. More specifically, cylindrically shaped reactors have been used to control a pH as multi-stages.
According to the prior art, a phosgene has been generally used 1.3 to 1.5 times more than total amounts of bisphenol-A and aliphatic diacid salt. Using a large amount of phosgen is not preferred to increase in a molecular weight of the polymer prepared from the oligomerization and polycondensation processes, since it produces a large amount of HCl to make lessen a pH of the reactor, and it also results in raising a production cost.
To solve these problems, the inventors have discovered a continuous preparation process for copolycarbonate, from which we have obtained a polycarbonate exhibiting a low melt viscosity than the commercial polycarbonates to mold an article more easily, and having excellent physical properties, and we can also obtain the polymer with high productivity and uniform quality. In particular, tube-type reactors are used to simplify the process (that is, cylindrically shaped batch-type reactor for reaction is generally used at two different ranges of pH, but in the present invention, serially connected two tube-type reactors are used for a continuous process), and variables such as Reynols Number, Linear Viscosity and Weber Number are regulated to increase the rate of reaction in order to achieve a novel polycondensation process involving an complete incorporation of comonomer into the polymer backbone.
A feature of the present invention is to provide a continuous process for preparing copolycarbonates suitable for molding articles of thin and complex structure due to their high melt flow.
Another feature of the present invention is to provide a continuous process for preparing copolycarbonate resins exhibiting an excellent transparency since unreacted reactants do not remain after the phosgenation reaction. In addition, the molding process of the copolycarbonate may be conducted at lower temperature (lower about 20xc2x0 C.) than that of a conventional polycarbonate, so the present invention may lead to an improved molding process.
Another feature of the present invention is to provide a continuous process, which is conducted with serially connected two tube-type reactors, in which a pH is fixed independently at a constant value while the reactors are sequentially used, compared with a conventional batch-type process, which includes a pH control at multi-stages for the phosgenation reaction. Therefore, the present invention excels in productivity of copolycarbonate resins exhibiting uniformity in quality.
Further feature of the present invention is to provide a continuous process in which only small amounts of phosgene are required and the rate of reaction is increased without remaining any unreacted reactants for preparing copolycarbonate resins.